U.S. patent application number 14/812792 was filed with the patent office on 2016-02-04 for intravascular ultrasound imaging apparatus, interface architecture, and method of manufacturing.
The applicant listed for this patent is Volcano Corporation. Invention is credited to Paul Douglas Corl.
Application Number | 20160029999 14/812792 |
Document ID | / |
Family ID | 54065408 |
Filed Date | 2016-02-04 |
United States Patent
Application |
20160029999 |
Kind Code |
A1 |
Corl; Paul Douglas |
February 4, 2016 |
Intravascular Ultrasound Imaging Apparatus, Interface Architecture,
and Method of Manufacturing
Abstract
Solid-state ultrasound imaging devices, systems, and methods are
provided. Some embodiments of the present disclosure are
particularly directed to compact and efficient ultrasound
transducer scanner formed from a substantially cylindrical
semiconductor substrate. In some embodiments, an intravascular
ultrasound (IVUS) device includes: an ultrasound scanner assembly
disposed at a distal portion of the flexible elongate member, the
ultrasound scanner assembly including a semiconductor substrate
having a plurality of transistors formed thereupon. The
semiconductor substrate is curved to have a substantially
cylindrical form when the ultrasound scanner assembly is in a
rolled form, and the plurality of transistors are arranged in a
cylindrical arrangement when the ultrasound scanner assembly is in
the rolled form. In one such embodiment, the device further
includes a plurality of ultrasound transducers formed upon the
semiconductor substrate and arranged in a cylindrical arrangement
when the ultrasound scanner assembly is in the rolled form.
Inventors: |
Corl; Paul Douglas; (Palo
Alto, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Volcano Corporation |
San Diego |
CA |
US |
|
|
Family ID: |
54065408 |
Appl. No.: |
14/812792 |
Filed: |
July 29, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62032368 |
Aug 1, 2014 |
|
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|
Current U.S.
Class: |
600/463 |
Current CPC
Class: |
A61B 8/445 20130101;
B06B 1/0633 20130101; A61B 8/56 20130101; A61B 8/5207 20130101;
A61B 8/12 20130101; A61B 8/4494 20130101 |
International
Class: |
A61B 8/08 20060101
A61B008/08; A61B 8/00 20060101 A61B008/00; A61B 8/12 20060101
A61B008/12 |
Claims
1. An ultrasound imaging device, comprising: a flexible elongate
member; and an ultrasound scanner assembly disposed at a distal
portion of the flexible elongate member, the ultrasound scanner
assembly including a semiconductor substrate having a plurality of
transistors formed thereupon, wherein the semiconductor substrate
is curved to have a substantially cylindrical form when the
ultrasound scanner assembly is in a rolled form, and wherein the
plurality of transistors are arranged in a cylindrical arrangement
when the ultrasound scanner assembly is in the rolled form.
2. The device of claim 1, wherein the plurality of transistors
includes transducer control circuitry, the device further
comprising: a plurality of ultrasound transducers formed upon the
semiconductor substrate and electrically coupled to the transducer
control circuitry, wherein the plurality of ultrasound transducers
are arranged in a cylindrical arrangement when the ultrasound
scanner assembly is in the rolled form.
3. The device of claim 2, wherein each transducer of the plurality
of ultrasound transducers includes a plurality of transducer
elements electrically connected in parallel.
4. The device of claim 3, wherein the plurality of transducer
elements includes CMUT transducer elements.
5. The device of claim 3, wherein the plurality of transducer
elements includes thin-film piezoelectric transducer elements.
6. The device of claim 2, wherein each transducer of the plurality
of ultrasound transducers includes at least two groups of
transducer elements, wherein the at least two groups of transducer
elements are independently addressable by the transducer control
circuitry.
7. The device of claim 1, wherein the semiconductor substrate
includes one of an elementary semiconductor substrate and a
compound semiconductor substrate, and wherein the one of the
elementary semiconductor substrate and the compound semiconductor
substrate is curved to have a cylindrical form when the ultrasound
scanner assembly is in the rolled form.
8. The device of claim 7, wherein the one of the elementary
semiconductor substrate and the compound semiconductor substrate is
formed to a thickness of less than or substantially equal to 10
.mu.m as measured when the ultrasound scanner assembly is in a flat
form.
9. The device of claim 2 further comprising an insulating layer
formed over the plurality of transistors and the plurality of
ultrasound transducers such that the insulating layer is outside
the plurality of transistors and the plurality of ultrasound
transducers when the ultrasound scanner assembly is in the rolled
form.
10. The device of claim 1, wherein the ultrasound scanner assembly
further includes a ferrule disposed within the cylindrical form of
the semiconductor substrate when the ultrasound scanner assembly is
in the rolled form.
11. The device of claim 10 further comprising an epoxy disposed
between the ferrule and the semiconductor substrate.
12. The device of claim 10, wherein the ferrule includes an inner
lumen adapted to pass a guide wire.
13. A scanner assembly for ultrasound imaging, the scanner assembly
comprising: a rollable semiconductor substrate; transducer control
logic formed on a control region of the rollable semiconductor
substrate; and a transducer formed on a transducer region of the
rollable semiconductor substrate and electrically coupled to the
transducer control logic, wherein the transducer control logic and
the transducer have a curved profile.
14. The scanner assembly of claim 13, wherein the rollable
semiconductor substrate includes a silicon semiconductor having a
curved profile.
15. The scanner assembly of claim 13, wherein the rollable
semiconductor substrate has a thickness of less than or
substantially equal to 10 .mu.m.
16. The scanner assembly of claim 13, wherein the transducer
includes a CMUT transducer comprising: a dielectric material formed
over the rollable semiconductor substrate; a vacuum gap formed
within a dielectric material; a diaphragm formed over the vacuum
gap; and an electrode formed over the diaphragm.
17. The scanner assembly of claim 16, wherein the diaphragm, the
vacuum gap, and the semiconductor substrate have a combined
thickness of less than or substantially equal to 10 .mu.m.
18. The scanner assembly of claim 17, wherein the vacuum gap has a
thickness substantially equal to 0.1 .mu.m.
19. The scanner assembly of claim 17, wherein the diaphragm has a
thickness substantially equal to 1 .mu.m.
20. The scanner assembly of claim 13, wherein the transducer
includes a piezoelectric micromachined ultrasound transducer (PMUT)
comprising: a chamber formed within the rollable semiconductor
substrate; and a piezoelectric film formed over the chamber.
21. The scanner assembly of claim 20, wherein the piezoelectric
film and the semiconductor substrate have a combined thickness of
between approximately 5 .mu.m and approximately 10 .mu.m.
22. The scanner assembly of claim 13 further comprising an outer
layer formed over the transducer control logic and the transducer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to and the benefit
of U.S. Provisional Patent Application No. 62/032,368, filed Aug.
1, 2014, which is hereby incorporated by reference in its
entirety.
TECHNICAL FIELD
[0002] The present disclosure relates generally to intravascular
ultrasound (IVUS) imaging and, in particular, to a solid-state IVUS
imaging system. In various embodiments, the IVUS imaging system
includes an array of ultrasound transducers, such as piezoelectric
zirconate transducers (PZTs), capacitive micromachined ultrasonic
transducers (CMUTs), and/or piezoelectric micromachined ultrasound
transducers (PMUTs), formed on a semiconductor substrate along with
associated control logic. The semiconductor substrate is then
rolled into a cylindrical form to form a scanner assembly and
disposed at a distal end of an intravascular elongate member. The
resulting device is suitable for advancing into an enclosed space
and imaging the surrounding structures. For example, some
embodiments of the present disclosure provide an IVUS imaging
system particularly suited to imaging a human blood vessel.
BACKGROUND
[0003] Intravascular ultrasound (IVUS) imaging is widely used in
interventional cardiology as a diagnostic tool for assessing a
diseased vessel, such as an artery, within the human body to
determine the need for treatment, to guide the intervention, and/or
to assess its effectiveness. An IVUS device includes one or more
ultrasound transducers arranged at a distal end of an elongate
member. The elongate member is passed into the vessel thereby
guiding the transducers to the area to be imaged. The transducers
emit ultrasonic energy in order to create an image of the vessel of
interest. Ultrasonic waves are partially reflected by
discontinuities arising from tissue structures (such as the various
layers of the vessel wall), red blood cells, and other features of
interest. Echoes from the reflected waves are received by the
transducer and passed along to an IVUS imaging system. The imaging
system processes the received ultrasound echoes to produce a
cross-sectional image of the vessel where the device is placed.
[0004] There are two general types of IVUS devices in use today:
rotational and solid-state (also known as synthetic aperture phased
array). For a typical rotational IVUS device, a single ultrasound
transducer element is located at the tip of a flexible driveshaft
that spins inside a plastic sheath inserted into the vessel of
interest. The transducer element is oriented such that the
ultrasound beam propagates generally perpendicular to the axis of
the device. The fluid-filled sheath protects the vessel tissue from
the spinning transducer and driveshaft while permitting ultrasound
signals to propagate from the transducer into the tissue and back.
As the driveshaft rotates, the transducer is periodically excited
with a high voltage pulse to emit a short burst of ultrasound. The
same transducer then listens for the returning echoes reflected
from various tissue structures. The IVUS imaging system assembles a
two dimensional display of the vessel cross-section from a sequence
of pulse/acquisition cycles occurring during a single revolution of
the transducer.
[0005] In contrast, solid-state IVUS devices utilize a scanner
assembly that includes an array of ultrasound transducers
distributed around the circumference of the device connected to a
set of transducer controllers. The transducer controllers select
transducer sets for transmitting an ultrasound pulse and for
receiving the echo signal. By stepping through a sequence of
transmit-receive sets, the solid-state IVUS system can synthesize
the effect of a mechanically scanned transducer element but without
moving parts. Since there is no rotating mechanical element, the
transducer array can be placed in direct contact with the blood and
vessel tissue with minimal risk of vessel trauma. Furthermore,
because there is no rotating element, the interface is simplified.
The solid-state scanner can be wired directly to the imaging system
with a simple electrical cable and a standard detachable electrical
connector.
[0006] Because an IVUS device is advanced into a confined space,
device agility, which strikes a balance between flexibility and
controllability, is an important characteristic. Rotational devices
tend to smoothly advance around corners due to the flexible
rotating drive shaft contained within the sheath. However,
rotational IVUS devices often require a long rapid exchange tip to
engage the guidewire, and the long tip may limit the advance of the
imaging core containing the transducer. For example, this may
prevent the device from being advanced to very distal locations
within the coronary arteries. On the other hand, solid-state IVUS
devices may have a shorter tip as the guidewire can pass through
the interior lumen of the scanner. However, some solid-state
designs have rigid segments that limit the ability to advance the
elongate member around sharp bends in the vasculature. Solid-state
IVUS devices also tend to be larger in diameter than rotational
devices to accommodate the transducer array and the associated
electronics.
[0007] While existing IVUS imaging systems have proved useful,
there remains a need for improvements in the design of the
solid-state scanner to reduce its overall diameter and to reduce
the length of rigid portions of the elongate member in order to
provide improved access to the vasculature. In addition, the
improvements to fabrication and assembly techniques would also
prove beneficial because of the difficulties inherent in assembling
miniscule components. Accordingly, the need exists for improvements
to the scanner assembly and its components, and to the methods used
in manufacturing these elements.
SUMMARY
[0008] Embodiments of the present disclosure provide a compact and
efficient scanner assembly in a solid-state imaging system.
[0009] In some embodiments, an intravascular ultrasound (IVUS)
device is provided. The device comprises: a flexible elongate
member; and an ultrasound scanner assembly disposed at a distal
portion of the flexible elongate member, the ultrasound scanner
assembly including a semiconductor substrate having a plurality of
transistors formed thereupon, wherein the semiconductor substrate
is curved to have a substantially cylindrical form when the
ultrasound scanner assembly is in a rolled form, and wherein the
plurality of transistors are arranged in a cylindrical arrangement
when the ultrasound scanner assembly is in the rolled form. In one
example, the device further comprises: a plurality of ultrasound
transducers formed upon the semiconductor substrate and
electrically coupled to the transducer control circuitry, wherein
the plurality of ultrasound transducers are arranged in a
cylindrical arrangement when the ultrasound scanner assembly is in
the rolled form.
[0010] In some embodiments, a scanner assembly for ultrasound
imaging is provided. The scanner assembly comprises a rollable
semiconductor substrate; transducer control logic formed on a
control region of the rollable semiconductor substrate; and a
transducer formed on a transducer region of the rollable
semiconductor substrate and electrically coupled to the transducer
control logic, wherein the transducer control logic and the
transducer have a curved form. In one such embodiment, the rollable
semiconductor substrate includes a silicon semiconductor having a
curved form.
[0011] In some embodiments, a method of manufacturing an
intravascular ultrasound device is provided. The method comprises:
receiving a semiconductor substrate; forming a transistor on the
semiconductor substrate; forming an ultrasound transducer on the
semiconductor substrate; and rolling the semiconductor substrate
having the transistor and the ultrasound transducer formed
thereupon to have a substantially cylindrical form, wherein the
rolling changes the profile of each of the transistor and the
ultrasound transducer. In one example, the method further
comprises: performing a process to change the semiconductor
substrate from a rigid state to a rollable state prior to the
rolling of the semiconductor substrate.
[0012] Some embodiments of the present disclosure utilize improved
fabrication techniques to reduce the diameter and length of the
scanner assembly. As the scanner assembly is rigid, decreasing the
size creates a more responsive device and may allow for a thinner
elongate member. The dimensions of a conventional scanner assembly
may be determined in part by the geometric challenges of arranging
flat elements such as controllers and transducers into a roughly
cylindrical device as well as the need for a transition zone to
accommodate differences in the cross-sectional shape along the
length of the cylinder. In contrast, in some embodiments of the
present disclosure, the transducers and control logic are formed on
a rollable substrate. During the rolling stage, the entire
substrate including the transducers and the control logic can be
curved to form a more cylindrical device. By utilizing space more
efficiently, the rollable substrate increases the device density
and decreases the size of the scanner assembly. By forming a more
uniform profile, the rollable substrate may permit a shorter
transition zone, further decreasing the length of the scanner
assembly along the longitudinal axis of the rolled assembly. The
resulting IVUS device is narrower and more flexible and, therefore,
able to maneuver through complicated vascular branches.
[0013] Some embodiments leverage the advantages of manufacturing
the elements of the scanner assembly on a single semiconductor
substrate to further reduce device size. Instead of dividing the
elements into discrete dies, separating the dies, and reassembling
them on a flexible interconnect, in the present embodiments, the
elements remain together on the semiconductor substrate throughout
the manufacture of the scanner assembly. This eliminates the
packaging bulk associated with multiple dies and may result in more
reliable interconnections. Furthermore, the yield loss associated
with dicing tiny components and bonding them to a flexible
interconnect is avoided. As a result, the manufacturing technique
simplifies assembly, reduces assembly time, and improves both yield
and device reliability.
[0014] Additional embodiments incorporate transducers that are
specially adapted to a flexible substrate. The transducers are
formed from an array of diaphragms or drumheads. As some flexible
substrates are relatively thin, the resonance chamber of each
diaphragm may be shallow. However, by connecting several diaphragms
in parallel, the effective size is much larger. This allows the
transducer to provide a more powerful ultrasonic signal while
transmitting and to produce a stronger electrical signal while
receiving. In addition, the operational frequency of a transducer
can be tuned by adjusting the number of diaphragms operating in
parallel. The result is a more sensitive transducer in a smaller
package.
[0015] Additional aspects, features, and advantages of the present
disclosure will become apparent from the following detailed
description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Illustrative embodiments of the present disclosure will be
described with reference to the accompanying drawings, of
which:
[0017] FIG. 1 is a diagrammatic schematic view of an intravascular
ultrasound (IVUS) imaging system according to an embodiment of the
present disclosure.
[0018] FIG. 2 is a flow diagram of a method of utilizing the IVUS
system according to an embodiment of the present disclosure.
[0019] FIG. 3 is a top view of a portion of an ultrasound scanner
assembly according to an embodiment of the present disclosure.
[0020] FIG. 4 is a cross-sectional view of a control region of an
ultrasound scanner assembly according to an embodiment of the
present disclosure.
[0021] FIG. 5 is a cross-sectional view of a transducer region of
an ultrasound scanner assembly according to an embodiment of the
present disclosure.
[0022] FIG. 6 is a longitudinal perspective view of a portion of an
ultrasound scanner assembly depicted in its rolled form according
to an embodiment of the present disclosure.
[0023] FIG. 7 is a top view of an ultrasound scanner assembly
incorporating a rollable semiconductor substrate according to an
embodiment of the present disclosure.
[0024] FIG. 8 is a cross-sectional view of a control region of an
ultrasound scanner assembly according to an embodiment of the
present disclosure.
[0025] FIG. 9 is a cross-sectional view of a transducer region of
an ultrasound scanner assembly according to an embodiment of the
present disclosure.
[0026] FIG. 10 is a longitudinal perspective view of a portion of
an ultrasound scanner assembly depicted in its rolled form
according to an embodiment of the present disclosure.
[0027] FIG. 11 is a flow diagram of the method of manufacturing an
ultrasound scanner assembly according to an embodiment of the
present disclosure.
[0028] FIGS. 12-16 are cross-sectional views of a scanner assembly
being manufactured by the method according to an embodiment of the
present disclosure.
[0029] FIG. 17 is a top view of a scanner assembly formed on a
wafer undergoing the method of manufacturing according to an
embodiment of the present disclosure.
[0030] FIGS. 18A and 18B are top views of a portion of a transducer
array according to an embodiment of the present disclosure.
[0031] FIG. 19 is a cross-sectional view of a portion of a
transducer incorporating an array of CMUT elements according to an
embodiment of the present disclosure.
[0032] FIG. 20 is a cross-sectional view of a portion of a
transducer incorporating an array of piezoelectric elements
according to an embodiment of the present disclosure.
DETAILED DESCRIPTION
[0033] For the purposes of promoting an understanding of the
principles of the present disclosure, reference will now be made to
the embodiments illustrated in the drawings, and specific language
will be used to describe the same. It is nevertheless understood
that no limitation to the scope of the disclosure is intended. Any
alterations and further modifications to the described devices,
systems, and methods, and any further application of the principles
of the present disclosure are fully contemplated and included
within the present disclosure as would normally occur to one
skilled in the art to which the disclosure relates. For example,
while the IVUS system is described in terms of cardiovascular
imaging, it is understood that it is not intended to be limited to
this application. The system is equally well suited to any
application requiring imaging within a confined cavity. In
particular, it is fully contemplated that the features, components,
and/or steps described with respect to one embodiment may be
combined with the features, components, and/or steps described with
respect to other embodiments of the present disclosure. For the
sake of brevity, however, the numerous iterations of these
combinations will not be described separately.
[0034] FIG. 1 is a diagrammatic schematic view of an ultrasound
imaging system 100 according to an embodiment of the present
disclosure. At a high level, an elongate member 102 (such as a
catheter, guide wire, or guide catheter) of the imaging system 100
is advanced into a vessel 104. The distal-most end of the elongate
member 102 includes a scanner assembly 106 with an array of
ultrasound transducers and associated control circuitry. When the
scanner assembly 106 is positioned near the area to be imaged, the
ultrasound transducers are activated and ultrasonic energy is
produced. A portion of the ultrasonic energy is reflected by the
vessel 104 and the surrounding anatomy and received by the
transducers. Corresponding echo information is passed along through
a Patient Interface Monitor (PIM) 108 to an IVUS console 110, which
renders the information as an image for display on a monitor
112.
[0035] The imaging system 100 may use any of a variety of
ultrasonic imaging technologies. Accordingly, in some embodiments
of the present disclosure, the IVUS imaging system 100 is a
solid-state IVUS imaging system incorporating an array of
piezoelectric transducers fabricated from lead-zirconate-titanate
(PZT) ceramic. In some embodiments, the system 100 incorporates
capacitive micromachined ultrasonic transducers (CMUTs), or
piezoelectric micromachined ultrasound transducers (PMUTs).
[0036] In some embodiments, the IVUS system 100 includes some
features similar to traditional solid-state IVUS system, such as
the EagleEye.RTM. catheter available from Volcano Corporation and
those disclosed in U.S. Pat. No. 7,846,101 hereby incorporated by
reference in its entirety. For example, the elongate member 102
includes the ultrasound scanner assembly 106 at a distal end of the
member 102, which is coupled to the PIM 108 and the IVUS console
110 by a cable 114 extending along the longitudinal body of the
member 102. The cable 114 caries control signals, echo data, and
power between the scanner assembly 106 and the remainder of the
IVUS system 100.
[0037] In an embodiment, the elongate member 102 further includes a
guide wire exit port 116. The guide wire exit port 116 allows a
guide wire 118 to be inserted towards the distal end in order to
direct the member 102 through a vascular structure (i.e., a vessel)
104. Accordingly, in some instances the IVUS device is a
rapid-exchange catheter. In an embodiment, the elongate member 102
also includes an inflatable balloon portion 120 near the distal
tip. The balloon portion 120 is open to a lumen that travels along
the length of the IVUS device and ends in an inflation port (not
shown). The balloon 120 may be selectively inflated and deflated
via the inflation port.
[0038] The PIM 108 facilitates communication of signals between the
IVUS console 110 and the elongate member 102 to control the
operation of the scanner assembly 106. This includes generating
control signals to configure the scanner, generating signals to
trigger the transmitter circuits, and/or forwarding echo signals
captured by the scanner assembly 106 to the IVUS console 110. With
regard to the echo signals, the PIM 108 forwards the received
signals and, in some embodiments, performs preliminary signal
processing prior to transmitting the signals to the console 110. In
examples of such embodiments, the PIM 108 performs amplification,
filtering, and/or aggregating of the data. In an embodiment, the
PIM 108 also supplies high- and low-voltage DC power to support
operation of the circuitry within the scanner assembly 106.
[0039] The IVUS console 110 receives the echo data from the scanner
assembly 106 by way of the PIM 108 and processes the data to create
an image of the tissue surrounding the scanner assembly 106. The
console 110 may also display the image on the monitor 112.
[0040] The ultrasound imaging system 100 may be utilized in a
variety of applications and can be used to image vessels and
structures within a living body. Vessel 104 represents fluid filled
or surrounded structures, both natural and man-made, within a
living body that may be imaged and can include for example, but
without limitation, structures such as: organs including the liver,
heart, kidneys, as well as valves within the blood or other systems
of the body. In addition to imaging natural structures, the images
may also include imaging man-made structures such as, but without
limitation, heart valves, stents, shunts, filters and other devices
positioned within the body.
[0041] FIG. 2 is a flow diagram of a method 200 of utilizing the
IVUS system 100 according to an embodiment of the present
disclosure. It is understood that additional steps can be provided
before, during, and after the steps of method 200, and that some of
the steps described can be replaced or eliminated for other
embodiments of the method.
[0042] Referring block 202 of FIG. 2 and referring still to FIG. 1,
in an illustrative example of a typical environment and application
of the system, a surgeon places a guide wire 118 in the vessel 104.
The guide wire 118 is threaded through at least a portion of the
distal end of the elongate member 102 either before, during, or
after placement of the guide wire 118. Referring to block 204 of
FIG. 2, once the guide wire 118 is in place, the elongate member
102 is advanced over the guide wire. Additionally or in the
alternative, a guide catheter is advanced in the vessel 104 in
block 202 and the elongate member 102 is advanced within the guide
catheter in block 204. Referring to block 206, once positioned, the
scanner assembly 106 is activated. Signals sent from the PIM 108 to
the scanner assembly 106 via the cable 114 cause transducers within
the assembly 106 to emit a specified ultrasonic waveform. The
ultrasonic waveform is reflected by the vessel 104. Referring to
block 208 of FIG. 2, the reflections are received by the
transducers within the scanner assembly 106 and are amplified for
transmission via the cable 114. The echo data is placed on the
cable 114 and sent to the PIM 108. The PIM 108 amplifies the echo
data and/or performs preliminary pre-processing, in some instances.
Referring to block 210 of FIG. 2, the PIM 108 retransmits the echo
data to the IVUS console 110. Referring to block 212 of FIG. 2, the
IVUS console 110 aggregates and assembles the received echo data to
create an image of the vessel 104 for display on the monitor 112.
In some exemplary applications, the IVUS device is advanced beyond
the area of the vessel 104 to be imaged and pulled back as the
scanner assembly 106 is operating, thereby exposing and imaging a
longitudinal portion of the vessel 104. To ensure a constant
velocity, a pullback mechanism is used in some instances. A typical
withdraw velocity is 0.5 mm/s. In some embodiments, the member 102
includes an inflatable balloon portion 120. As part of a treatment
procedure, the device may be positioned adjacent to a stenosis
(narrow segment) or an obstructing plaque within the vessel 104 and
inflated in an attempt to widen the restricted area of the vessel
104.
[0043] The system 100, and in particular the elongate member 102,
is designed to provide high-resolution imaging from within narrow
passageways. To advance the performance of IVUS imaging devices
compared to the current state of the art, embodiments of the
present disclosure have improved flexibility and reduced diameter
allowing greater maneuverability and leading to increased patient
safety and comfort. While the elongate member 102 is generally
flexible, it may include components within it that are not. For
example, the ultrasound scanner assembly 106 is often rigid. As a
result, the scanner assembly 106 may limit the agility of the
elongate member 102 and may make navigating the vessel 104 more
difficult. In addition, the bulk of the ultrasound transducers and
the associated circuitry in the scanner assembly 106 may make it a
limiting factor in the drive towards a smaller-gauge elongate
member 102. For these reasons and others, an ultrasound scanner
assembly 106 that is smaller longitudinally and circumferentially,
as provided herein, may allow for a thinner elongate member 102
with improved agility to navigate complex vessels 104. Specific
embodiments also provide faster, less expensive, and more reliable
methods of manufacturing the scanner assembly 106.
[0044] FIG. 3 is a top view of a portion of an ultrasound scanner
assembly 106 according to an embodiment of the present disclosure.
FIG. 3 depicts the ultrasound scanner assembly 106 in its flat
form. The assembly 106 includes a transducer array 302 formed in a
transducer region 304 and transducer control logic dies 306
(including dies 306A and 306B) formed in a control region 308, with
a transition region 310 disposed therebetween. With respect to the
transducer array 302, the array 302 may include any number and type
of ultrasound transducers 312, although for clarity only a limited
number of ultrasound transducers are illustrated in FIG. 3. In an
embodiment, the transducer array 302 includes 64 individual
ultrasound transducers 312. In a further embodiment, the transducer
array 302 includes 32 ultrasound transducers 312. Other numbers are
both contemplated and provided for. With respect to the types of
transducers, in an embodiment, the ultrasound transducers 312 are
piezoelectric micromachined ultrasound transducers (PMUTs)
fabricated on a microelectromechanical system (MEMS) substrate
using a polymer piezoelectric material, for example as disclosed in
U.S. Pat. No. 6,641,540, which is hereby incorporated by reference
in its entirety. In alternate embodiments, the transducer array
includes piezoelectric transducers fabricated from bulk PZT ceramic
or single crystal piezoelectric material, piezoelectric
micromachined ultrasound transducers (PMUTs), capacitive
micromachined ultrasound transducers (CMUTs), other suitable
ultrasound transmitters and receivers, and/or combinations
thereof.
[0045] The scanner assembly 106 may include various transducer
control logic, which in the illustrated embodiment is divided into
discrete control logic dies 306. In various examples, the control
logic of the scanner assembly 106 performs: decoding control
signals sent by the PIM 108 across the cable 114, driving one or
more transducers 312 to emit an ultrasonic signal, selecting one or
more transducers 312 to receive a reflected echo of the ultrasonic
signal, amplifying a signal representing the received echo, and/or
transmitting the signal to the PIM across the cable 114. In the
illustrated embodiment, a scanner assembly 106 having 64 ultrasound
transducers 312 divides the control logic across nine control logic
dies 306, of which five are shown. Designs incorporating other
numbers of control logic dies 306 including 8, 9, 16, 17 and more
are utilized in other embodiments. In general, the control logic
dies 306 are characterized by the number of transducers they are
capable of driving, and exemplary control logic dies 306 drive 4,
8, and 16 transducers.
[0046] The control logic dies are not necessarily homogenous. In
some embodiments, a single controller is designated a master
control logic die 306A and contains the communication interface for
the cable 114. Accordingly, the master control circuit may include
control logic that decodes control signals received over the cable
114, transmits control responses over the cable 114, amplifies echo
signals, and/or transmits the echo signals over the cable 114. The
remaining controllers are slave controllers 306B. The slave
controllers 306B may include control logic that drives a transducer
312 to emit an ultrasonic signal and selects a transducer 312 to
receive an echo. In the depicted embodiment, the master controller
306A does not directly control any transducers 312. In other
embodiments, the master controller 306A drives the same number of
transducers 312 as the slave controllers 306B or drives a reduced
set of transducers 312 as compared to the slave controllers 306B.
In an exemplary embodiment, a single master controller 306A and
eight slave controllers 306B are provided with eight transducers
assigned to each slave controller 306B.
[0047] The transducer control logic dies 306 and the transducers
312 are mounted on a flex circuit 314 that provides structural
support and interconnects for electrical coupling. The flex circuit
314 may be constructed to include a film layer of a flexible
polyimide material such as KAPTON.TM. (trademark of DuPont). Other
suitable materials include polyester films, polyimide films,
polyethylene napthalate films, or polyetherimide films, other
flexible printed semiconductor substrates as well as products such
as Upilex.RTM. (registered trademark of Ube Industries) and
TEFLON.RTM. (registered trademark of E.I. du Pont). The film layer
is configured to be wrapped around a ferrule to form a cylindrical
toroid in some instances. Therefore, the thickness of the film
layer is generally related to the degree of curvature in the final
assembled scanner assembly 106. In some embodiments, the film layer
is between 5 .mu.m and 100 .mu.m, with some particular embodiments
being between 12.7 .mu.m and 25.1 .mu.m.
[0048] To electrically interconnect the control logic dies 306 and
the transducers, in an embodiment, the flex circuit 314 further
includes conductive traces formed on the film layer that carry
signals between the control logic dies 306 and the transducers 312
and that provide a set of pads for connecting the conductors of
cable 114. Suitable materials for the conductive traces include
copper, gold, aluminum, silver, nickel, and tin and may be
deposited on the flex circuit 314 by processes such as sputtering,
plating, and etching. In an embodiment, the flex circuit 314
includes a chromium adhesion layer or a titanium-tungsten adhesion
layer. The width and thickness of the conductive traces are
selected to provide proper conductivity and resilience when the
flex circuit 314 is rolled. In that regard, an exemplary range for
the width of a conductive trace is between 10-50 .mu.m. For
example, in an embodiment, 20 .mu.m conductive traces are separated
by 20 .mu.m of space. The width of a conductive trace may be
further determined by the size of a pad of a device or the width of
a wire to be coupled to the trace. The thickness of the conductive
traces may have a range from about 1 .mu.m to about 10 .mu.m, with
a typical thickness of 5 .mu.m.
[0049] In some instances, the scanner assembly 106 is transitioned
from a flat configuration to a rolled or more cylindrical
configuration. For example, in some embodiments, techniques are
utilized as disclosed in one or more of U.S. Pat. No. 6,776,763,
titled "ULTRASONIC TRANSDUCER ARRAY AND METHOD OF MANUFACTURING THE
SAME" and U.S. Pat. No. 7,226,417, titled "HIGH RESOLUTION
INTRAVASCULAR ULTRASOUND TRANSDUCER ASSEMBLY HAVING A FLEXIBLE
SUBSTRATE," each of which is hereby incorporated by reference in
its entirety.
[0050] FIG. 4 is a cross-sectional view of a control region 308 of
an ultrasound scanner assembly 106 according to an embodiment of
the present disclosure. The control region 308 is depicted in its
rolled form and contains the transducer control logic dies 306
bonded to the flex circuit 314. In the illustrated embodiment, the
flex circuit 314 also includes a conductive ground layer 402. In a
further embodiment, the flex circuit includes an outer membrane 404
used to insulate and cover the ground layer 402 and to protect the
scanner assembly 106 from the environment. Insulator materials for
the outer membrane 404 may be selected for their biocompatibility,
durability, hydrophilic or hydrophobic properties, low-friction
properties, ultrasonic permeability, and/or other suitable
criteria. For example, the outer membrane may include Parylene.TM.
(trademark of Union Carbide). Other suitable materials include heat
shrink tubing such as polyester or PVDF, a melt-formable layers
such as Pebax.RTM. (registered trademark of Arkema) or
polyethylene, and/or other suitable membrane materials.
[0051] As discussed above, in many embodiments, the flex circuit
314 and the attached elements are rolled around a ferrule 406. The
lumen region 408 inside the ferrule 406 is open to allow the
scanner assembly 106 to be advanced over a guide wire (not shown).
The ferrule 406 may include a radiopaque material to aid in
visualizing the scanner assembly 106 during a procedure. In some
instances, encapsulating epoxy 410 fills the spaces between the
control logic dies 306 and the ferrule 406.
[0052] In some embodiments, the control logic dies 306 are coupled
to the flex circuit 314 by contact bumps 412. The contact bumps 412
may include a metal core, such as a copper core, with a solder
portion. During formation, the contact may be heated, causing the
solder to flow and join the metal core of the contact bump 412 to
the flex circuit 314 trace. An underfill material 414 between the
control logic dies 306 and the flex circuit 314 may be applied to
increase the bond strength, to provide structural support for the
control region 308, to insulate conductive structures including the
contact bumps 412, and/or to promote thermal conduction.
[0053] In an embodiment, the control region 308 includes a
retaining structure 416 applied over the transducer control logic
dies 306. The retaining structure 416 may be used during the
rolling process, for example, to secure components including the
control logic dies 306. Encapsulating epoxy 410 fills the space
between the transducer control logic dies 306 and the retaining
structure 416 and between the retaining structure 416 and the
ferrule 406 in some embodiments.
[0054] As can be seen from FIG. 4, the transducer control logic
dies 306 at least partially define the shape of the control region
308. In the illustrated embodiment, because the transducer control
logic dies 306 are rigid, the portions of the flex circuit 314
adjacent to the control logic dies 306 are relatively flat while
the portions of the flex circuit adjacent gaps between the dies 306
are relatively rounded, resulting in a cross-sectional shape that
is more polygonal than circular. As can be seen, the gaps between
control logic dies 306 in the rolled configuration increase the
effective diameter 418 of the control region 308. In some
embodiments, half of the circumference of the control region 308 is
due to gap space. The result is a larger and more irregular shaped
scanner assembly 106.
[0055] To reduce the gap space, in some embodiments, the control
logic dies 306 include interlocking teeth. For example, control
logic dies 306 may be formed with a recess and projection that
interlocks with a recess and projection of an adjacent control
logic die 306 to form a box joint or finger joint. In the
illustrated embodiment, each of the dies 306 interlocks with two
adjacent controllers utilizing a recess and projection interface.
In some embodiments, a control logic die 306 includes a chamfered
edge, either alone or in combination with a recess and projection.
The chamfered edge may be configured to abut an edge of an adjacent
control logic die 306. In some such embodiments, the edge of the
adjacent controller is chamfered as well. Other combinations,
including embodiments utilizing a number of different mechanisms,
are contemplated and provided for. Edge configurations that
interlock adjacent control logic dies 306 may allow for closer
control logic die spacing and a reduced diameter 418 in the rolled
configuration. Such configurations may also interlock to create a
rigid structure and thereby provide additional structural support
for the rolled scanner assembly 106. Additionally or in the
alternative, narrower and more numerous control logic dies 306 are
used in place of larger dies in order to reduce the size of the
flat areas of the controller region 308. It follows that designs
utilizing 8, 9, 16, or more transducer control logic dies 306 have
a more circular cross-section than designs with 4 or 5
controllers.
[0056] FIG. 5 is a cross-sectional view of a transducer region 304
of an ultrasound scanner assembly 106 according to an embodiment of
the present disclosure. The transducer region 304 is depicted in
its rolled form. As the name implies, the transducer region 304 of
the scanner contains the transducers 312, which, as previously
disclosed, are physically attached to the flex circuit 314 and are
electrically coupled to the traces of the flex circuit 314. As can
be seen, the size, shape, and spacing of the ultrasound transducers
312 at least partially define the shape of the transducer region
304, with the portions of the flex circuit 314 that are adjacent to
the transducers 312 being relatively flat and the portions of the
flex circuit that are adjacent gaps between transducers 312 being
relatively rounded. Due in part to the smaller size and greater
number of transducers 312, the transducer region 304 may be more
circular than the control region 308. In embodiments with 64
ultrasound transducers 312, the cross-section of the transducer
region 304 is nearly circular.
[0057] To accommodate the difference between the cross-sectional
shapes of the transducer region 304 and the control region 308, the
scanner assembly 106 may include a transition region 310 as shown
in FIG. 6. FIG. 6 is a longitudinal perspective view of a portion
of an ultrasound scanner assembly 106 depicted in its rolled form
according to an embodiment of the present disclosure. Referring to
FIG. 6, the transition region 310 is located between the transducer
region 304 and the control region 308. In contrast to the
transducer region 304 and the control region 308, the transition
region 310 is free of rigid structures. Instead, the
cross-sectional shape is defined by the adjacent regions 304 and
308. Thus, the shape of the transition region 310 transitions
between that of the transducer region 304 and the controller region
308. The transition region 310 may be used to reduce sharp angles
that can stress the flex circuit 314 and/or the conductive traces.
Greater differences in cross-sectional shapes may result in a
longer transition region 310. In an exemplary four-control logic
die embodiment, the transition region 310 is approximately 1 to 1.5
catheter diameters in order to transition from square to
substantially round. This works out to be between 1000 and 1500
.mu.m for a 3Fr catheter. In contrast, in an exemplary nine-control
logic die embodiment, the transition region 310 is approximately
0.5 to 0.75 catheter diameters, or between 500 and 750 .mu.m for a
3Fr catheter. Because the scanner assembly 106 (including the
transition region 310) is typically inflexible or rigid compared to
the surrounding portion of the device, reducing the length of the
transition region 310 results in a more agile IVUS device capable
of maneuvering through complex vascular branches and producing less
discomfort in the patient.
[0058] Another technique for reducing the size of the scanner
assembly includes manufacturing the transducers and/or the control
circuitry on a rollable semiconductor substrate. This reduces the
irregularity caused by the flat transducers 312 and control logic
dies 306 of the previous examples, and may reduce both the
longitudinal length and the diameter of the scanner assembly. FIG.
7 is a top view of an ultrasound scanner assembly 700 incorporating
a rollable semiconductor substrate according to an embodiment of
the present disclosure. FIG. 7 depicts the ultrasound scanner
assembly 700 in its flat form. In many respects, the ultrasound
scanner assembly 700 may be substantially similar to scanner
assembly 106 of FIGS. 3-6 and may include a transducer array 702
that includes any number any number and type of ultrasound
transducers 703 formed in a transducer region 704. In an exemplary
embodiment, the transducer array 702 includes 64 CMUT transducers
703. The ultrasound scanner assembly 700 may also include control
logic circuitry 706 formed in a control region 708 with a
transition region 710 disposed therebetween. The ultrasound scanner
assembly 700 may also include contact pads 712 for coupling the
scanner assembly 700 to a cable 114 for communication with other
components of an IVUS system such as a PIM 108. However, whereas
the transducers 312 and control logic dies 306 of FIG. 3, for
example, are formed on a rigid substrate, the transducer array 702
and the control circuitry 706 of the present embodiment are formed
on a rollable substrate 714. Thus, the elements of the scanner
assembly 700 may be shaped into a curve as indicated by arrow 716
and many of the challenges involved in arranging flat components
into a roughly circular profile are avoided. As a result, the
transducer region 704 and the control region 708 have a more
circular cross-sectional shape in the rolled configuration, as
shown in more detail in the context of FIGS. 8 and 9.
[0059] Furthermore, for reasons discussed in more detail below, the
overall size of the scanner assembly may be reduced 700. In brief,
by eliminating the gaps between discrete dies, the diameter of the
scanner assembly (and correspondingly the circumference and gauge)
may be reduced. In addition, because the profiles of the control
region 708 and the transducer regions 704 are similar, a shorter
transition region 710 may be utilized thereby reducing the
longitudinal length of the scanner assembly 700. In embodiments
where the transition region 710 is not used to transition between
the profiles of the control region 708 and the transducer region
704, the shorter transition region 710 may still prove useful as a
sacrificial region during dicing. In an exemplary embodiment, the
control region 708 measures approximately 1.5 mm in the Y
direction, the transition region 710 measures approximately 1 mm in
the Y direction, and the transducer region 704 measures between
approximately 0.75 mm and 0.5 mm in the Y direction.
[0060] FIG. 8 is a cross-sectional view of a control region 708 of
an ultrasound scanner assembly 700 according to an embodiment of
the present disclosure. The control region 708 is illustrated in
its rolled form and includes the control circuitry 706 formed on a
rollable semiconductor substrate 714. As can be seen, the
semiconductor substrate 714 is flexed to form a cylinder and more
specifically, a cylindrical toroid. The resulting cross-sectional
profile of the control region 708 is substantially circular without
flat regions seen in other examples. By eliminating gap space
between dies and protrusions caused by flat dies, the control
circuitry 706 may be packed more densely. Because dies often
include reserved areas for separating dies during manufacturing
(scribe lines), device density may be further improved by using a
single rollable substrate 714. Similarly, dies often include
insulators, pads, and other bulk that may be eliminated through the
use of a rollable substrate 714.
[0061] In addition, the amount of control circuitry 706 may be
reduced when compared to embodiments utilizing discrete dies. For
example, partitioning the control circuitry 706 across dies often
involves duplicating functionality. This duplicate logic may be
avoided in embodiments where the control circuitry 706 remains
together. As yet another example, partitioning the control
circuitry 706 across dies often involves adding large and power
hungry I/O circuitry to transmit, synchronize, and amplify signals
between dies. This too may be avoided in embodiments where the
control circuitry 706 remains together on the semiconductor
substrate 714. Furthermore, transmitting analog signals between
dies, such as echo data, may introduce noise. For these reasons and
others, the control region 708 incorporating a flexible substrate
714 may be smaller and more efficient than other configurations and
may provide greater imaging fidelity. In particular, the control
region 708 may have a smaller diameter 804 and may have a
corresponding gauge less than 3Fr.
[0062] In contrast to previous examples, by rolling the substrate
714, the devices formed on the substrate 714 (i.e., the transistors
of the control circuitry 706) become curved and rearranged in a
cylindrical arrangement. To account for this, the devices may be
oriented on the substrate 714 in such a manner as to reduce stress
and the possibility of cracking when rolled. For example, the
devices may be aligned such that the gate width direction extends
along the longitudinal axis of the substrate 714 in the rolled
form. In some embodiments, the active regions and the gate
structures of the control circuitry 706 are arranged on the outer
surface of the substrate 714 when in the rolled form, whereas in
other embodiments, the active regions and the gate structures are
arranged on the inner surface of the substrate when in the rolled
form.
[0063] In the illustrated embodiment, the control region 708
includes an outer jacket 802 used to insulate the rollable
semiconductor substrate 714 and to protect the scanner assembly 700
from the environment. The insulator materials for the outer jacket
802 may be selected for their biocompatibility, durability,
hydrophilic or hydrophobic properties, low-friction properties,
ultrasonic permeability, and/or other suitable criteria. In various
embodiments, the outer jacket 802 includes KAPTON.TM., polyester
films, polyimide films, polyethylene napthalate films, and/or
Upilex.RTM.. In further embodiments, the outer jacket 802 includes
Parylene.TM., heat shrink tubing such as polyester or PVDF, a
melt-formable layers such as Pebax.RTM. (registered trademark of
Arkema) or polyethylene, and/or other suitable membrane materials.
In some embodiments, the outer jacket 802 includes a flexible
circuit, such as a polyimide or liquid crystal polymer-based
flexible circuit. The flexible circuit may be further jacketed by a
shrink fit or other jacket material. A wide variety of suitable
shrink-fit materials exist including polyester and/or Pebax.RTM..
In an exemplary embodiment, a layer of the outer jacket 802 is
formed with proper thickness and acoustic impedance to act as a
matching layer for ultrasound signals. The matching layer typically
has an acoustic impedance between that of the ultrasound transducer
and the surrounding vessel and provides a smoother acoustic
transition with reduced reflections.
[0064] In some instances, the control region 708 is formed around a
ferrule 406 and includes an encapsulating epoxy 410 filling the
space between the semiconductor substrate 714 and the ferrule 406.
The lumen region 408 inside the ferrule 406 is open to allow the
scanner assembly 700 to be advanced over a guide wire (not shown).
The ferrule 406 may include a radiopaque material to aid in
visualizing the scanner assembly 700 during a procedure.
[0065] FIG. 9 is a cross-sectional view of a transducer region 704
of an ultrasound scanner assembly 700 according to an embodiment of
the present disclosure. The transducer region 704 is depicted in
its rolled form and includes a transducer array 702 formed on a
rollable semiconductor substrate 714. The transducer array 702
includes any number any number and type of ultrasound transducers
703, and in an exemplary embodiment includes 64 CMUT transducers.
As in the control region 708, the semiconductor substrate 714 is
flexed to form a cylinder or cylindrical toroid and the resulting
cross-sectional profile of the transducer region 704 is
substantially circular. Similar to the control region 708, the
transducers of the transducer array 702 become curved and take on a
cylindrical arrangement. In an exemplary embodiment, the
transducers of the transducer array 702 are arranged on the outer
surface of the substrate 714 when in the rolled form.
[0066] FIG. 10 is a longitudinal perspective view of a portion of
an ultrasound scanner assembly 700 depicted in its rolled form
according to an embodiment of the present disclosure. The scanner
assembly 700 includes a transition region 710 located between the
transducer region 704 and the control region 708. As can be seen,
the cross-sectional profiles of the transducer region 704 and the
control region 708 are similar and thus the transition region 710
may be shorter in the longitudinal direction as compared to the
previous examples. For a variety of reasons, including those
discussed above, the gauge or thickness of the rolled scanner
assembly 700 may be less than that of other configurations. For
example, in various embodiments, the scanner assembly 700 is
between 2-3Fr and, in a specific embodiment, the scanner assembly
700 measures approximately 2Fr.
[0067] A method of forming an ultrasound scanner assembly 700
incorporating a rollable semiconductor substrate 714 is described
with reference to FIGS. 11-17. FIG. 11 is a flow diagram of the
method 1100 of manufacturing the ultrasound scanner assembly 700
according to an embodiment of the present disclosure. It is
understood that additional steps can be provided before, during,
and after the steps of method 1100 and that some of the steps
described can be replaced or eliminated for other embodiments of
the method. FIGS. 12-16 are cross-sectional views of a scanner
assembly 700 being manufactured by the method according to an
embodiment of the present disclosure. FIGS. 12-16 each show
transducer control circuitry 706 being manufactured in a control
region 708 and a transducer array 702 being manufactured in a
transducer region 704. FIG. 17 is a top view of a scanner assembly
700 formed on a wafer undergoing the method of manufacturing
according to an embodiment of the present disclosure.
[0068] Referring to block 1102 of FIG. 11 and to FIG. 12, a
semiconductor substrate 714 is received. Substrate 714 may be any
base material on which processing is conducted to produce layers of
materials, pattern features, and/or integrated circuits such as
those used to manufacture transducer control circuitry 706.
Examples of semiconductor substrates include a bulk silicon
substrate, an elementary semiconductor substrate such as a silicon
or germanium substrate, a compound semiconductor substrate such as
a silicon germanium substrate, an alloy semiconductor substrate,
and substrates including non-semiconductor materials such as glass
and quartz.
[0069] Referring to block 1104 of FIG. 11 and referring still to
FIG. 12, transistors of the control circuitry 706 are formed on the
substrate 714 in the control region 708. An exemplary process for
forming the transistors includes growing a pad oxide layer over the
substrate, depositing a nitride layer by chemical vapor deposition,
performing a reactive ion etching to form a trench, growing a
shallow trench isolation feature oxide, chemical-mechanical
planarization, channel implantation, formation of a gate oxide,
polysilicon deposition, etching to form a gate structure,
source-drain implantation, forming of sidewall spacers, performing
a self-aligned silicide process, forming one or more interconnect
layers, forming a pad layer, and/or other fabrication processes
known to one of skill in the art. In some instances, the process
for forming the control circuitry 706 produces gate structures
1202, shallow trench isolation features 1204, conductive
interconnects 1206, and insulator layers 1208.
[0070] Referring to block 1106 of FIG. 11 and to FIGS. 13-15, one
or more transducers of the transducer array 702 are formed on the
substrate 714. The present disclosure is not limited to any
particular transducer technology, and while the illustrated
embodiment includes CMUT transducers, other embodiments incorporate
thin-film PZT transducers, PMUT transducers, and/or other
transducer types. Referring to FIG. 13, in one example, CMUT
transducers are formed in block 1106 by depositing a dielectric
layer 1302 on the substrate 714 and depositing a sacrificial layer
1304, such as a polysilicon layer, on the dielectric layer 1302 to
define the CMUT vacuum gap, which acts as a resonance chamber.
Referring to FIG. 14, further dielectric material 1402 is deposited
over the sacrificial layer 1304 with holes formed therein to allow
the sacrificial layer 1304 to be etched. Referring to FIG. 15, the
sacrificial layer 1304 is etched away from underneath the
dielectric and the holes are filled with additional dielectric
material 1402. This may be performed in a vacuum so that the
remaining cavity is a vacuum gap 1502 within the dielectric
formation of 1302 and 1402.
[0071] The material over the vacuum gap 1502 is referred to as a
diaphragm 1504 or drumhead and is free to deflect into the vacuum
gap 1502. An electrode 1506 is formed over the vacuum gap that
together with a conductive region of the substrate 714 form a
parallel plate capacitor. Deflection of the diaphragm 1504 and the
electrode 1506 into the vacuum gap, such as deflection caused by an
ultrasonic wave, changes the electrical behavior of the capacitor.
These changes can be measured in order to determine properties of
the wave that caused them. One or more interconnect layers 1206
and/or passivation layers 1208 may then be formed over the
electrode 1506.
[0072] Referring to block 1108 of FIG. 11 and to FIG. 15, a polymer
coating such as the outer jacket 802 described in FIG. 8 may be
formed on the substrate 714 and insulates the control circuitry 706
and the transducer array 702. Additionally or in the alternative,
the outer jacket 802 may be formed over the substrate 714 after the
rolling of the substrate 714 during the final assembly in block
1116, described below.
[0073] Referring to block 1110 of FIG. 11 and to FIG. 16, the
substrate 714 is made rollable. In other words, while the finished
substrate 714 may be flexible enough to be rolled, the substrate
714 in its initial form may be rigid for easier manufacturing of
the transducer array 702 and the control circuitry 706. In some
embodiments, the substrate 714 is made rollable by performing a
thinning process. For example, in some embodiments, thinning the
substrate 714 to a thickness of approximately 10 .mu.m or less
results in a substrate 714 that is flexible enough to be rolled.
Suitable thinning processes include mechanical grinding, wet or dry
etching, chemical-mechanical polishing, fracturing, and/or
otherwise thinning the substrate 714. In an embodiment, the wafer
thinning process includes mechanical grinding of the substrate 714.
Mechanical grinding uses abrasive force to remove substrate
material. In another embodiment, the wafer thinning process
includes chemical-mechanical polishing (CMP). In an exemplary CMP
process, a polishing pad is installed on a rotating platen. A
slurry of reactive compounds such as NH4OH and/or abrasive
particles such as silica (SiO2), alumina (Al2O3), and ceria (CeO2)
is dispensed on the polishing pad. The substrate 714, secured in a
CMP chuck, is forced against the polishing pad as both the platen
and the CMP chuck rotate. The reactants in the slurry loosen atomic
bonds within the surface of the substrate 714, while the mechanical
abrasion removes the loosened material. CMP is typically slower
than purely mechanical grinding but produces less damage to the
substrate 714.
[0074] In some embodiments, the substrate 714 includes one or more
buried layers to control the thinning of the substrate 714. For
example, in an embodiment, the substrate 714 includes a dielectric
layer that acts as a stop layer during a mechanical grinding
process. In a further example, the substrate 714 includes a buried
dielectric layer (e.g., a buried oxide layer) that acts as an etch
stop layer during a chemical etching process. In yet a further
example, the substrate 714 includes a cleavage layer that separates
from the remainder of the substrate 714 during a mechanical
separation process.
[0075] Referring to block 1112 of FIG. 11 and to FIG. 17, the
transducer array 702 and the control circuitry 706 of the scanner
assembly 700 are singulated from a wafer 1702. As can be seen,
several scanner assemblies 700 can be formed on a single wafer
1702. For example, approximately two thousand scanner assemblies
700 each measuring 10 mm.sup.2 may be formed on a single 8'' wafer
1702. Before being rolled, the scanner assemblies 700 are separated
using techniques that may include saw dicing, mechanical cutting,
laser cutting, physical force, and/or other suitable singulation
techniques.
[0076] Referring to block 1114 of FIG. 11, the scanner assembly 700
is rolled to have a substantially cylindrical form as shown in
FIGS. 8-10. Because the rolling process curves the transistors of
the control circuitry 706 and the transducers 703 of the transducer
array 702, flat areas and other irregularities are reduced. In some
embodiments, rolling includes applying a retaining structure 416
before the scanner assembly 700 is shaped into the substantially
cylindrical form.
[0077] Referring to block 1116 of FIG. 11, the scanner assembly 700
is provided to a finishing facility for final assembly, which may
include applying an encapsulating epoxy 410, attaching the cable
114, and/or sealing the scanner assembly 700. Thus, the use of a
rollable semiconductor substrate 714 in method 1100 eliminates the
complexity and yield loss associated with dicing tiny components
and bonding them to a flexible interconnect. As a result, the
manufacturing technique simplifies assembly, reduces assembly time,
and improves both yield and device reliability.
[0078] As disclosed above, the scanner assembly 700 may incorporate
any suitable ultrasound transducer technology, including the CMUT
transducer 703 illustrated in FIG. 16. Suitable transducers 703 are
illustrated in further detail in FIGS. 18A, 18B, 19, and 20. FIGS.
18A and 18B are top views of a portion of a transducer array 702
according to an embodiment of the present disclosure. FIG. 18B is
an enlarged view of the portion. FIG. 19 is a cross-sectional view
of a portion of a transducer 703 incorporating an array of CMUT
elements 1902 according to an embodiment of the present disclosure.
FIG. 20 is a cross-sectional view of a portion of a transducer 703
incorporating an array of piezoelectric elements 2002 according to
an embodiment of the present disclosure.
[0079] Referring first to FIGS. 18A and 18B, in the illustrated
embodiment, each transducer 703 of the transducer array 702
includes an array of transducer elements 1802. Each element 1802 is
itself a transducer operable to generate a waveform by vibrating a
diaphragm 1504 (i.e., a drumhead) and to produce an electrical
signal in response to a received waveform. In that regard, each
element 1802 may include a diaphragm 1504, a chamber such as a
vacuum gap 1502, an associated electrode 1506, and/or any other
ancillary structure. Because of the limited displacement of each
element 1802, each transducer 703 may include multiple elements
1802 electrically connected in parallel to increase the effective
surface area. For example, the electrodes 1506 of multiple
diaphragms 1504 may be connected by a common interconnect (e.g.,
interconnects 1206A and 1206B). In this way, the transducers 703
can compensate for a thinner substrate 714 and correspondingly
shallower vacuum gaps. In the illustrated embodiment, each
diaphragm 1504 is substantially circular with a diameter of
approximately 10 .mu.m, although it is understood in further
embodiments the transducers 703 include other sizes and shapes of
diaphragm 1504. In the interest of clarity, the number of elements
1802 has been reduced, and while each transducer 703 may include
any number of elements 1802, in an exemplary embodiment, each
transducer 703 includes approximately 100 elements.
[0080] In addition to providing a large effective surface area, an
array of elements 1802 can be tuned to more than one frequency by
adjusting the number of elements 1802 operating in unison. An array
can also produce specialized waveforms by adjusting the firing
sequence of the elements 1802. Accordingly, in some embodiments,
elements 1802 of a transducer 703 are arranged into groups
(indicated by dashed boxes 1804). While the elements 1802 of each
group are electrically connected in parallel and thus operate in
unison, the groups can be independently controlled or addressed to
produce a number of different ultrasonic waveforms at a number of
different characteristic frequencies. Thus, a single transducer 703
can support multiple imaging modes, with common modes including
both 20 MHz and 40 MHz modes.
[0081] Referring now to FIG. 19, a portion of a transducer 703 is
shown. In the embodiment, the transducer 702 includes CMUT
transducer elements 1902. The three illustrated elements each
include a vacuum gap 1502 defined by a dielectric layer 1302 formed
on the substrate 714, a diaphragm 1504 formed over the vacuum gap
1502, an electrode 1506 formed over the diaphragm, and an
interconnect 1206 electrically coupling the diaphragms 1504 to
other diaphragms 1504 and to the control circuitry (not shown).
[0082] As can be seen, the CMUT transducer elements 1902 are well
suited for the rollable substrate 714 because their overall profile
can be quite thin. For example, in an embodiment, the combined
thickness 1904 of the diaphragm 1504, the vacuum gap 1502, and the
substrate 714 is less than or substantially equal to 10 .mu.m. In
the embodiment, the diaphragm 1504 has a thickness of approximately
1 .mu.m, and the vacuum gap 1502 has a thickness of approximately
0.1 .mu.m.
[0083] Referring to FIG. 20, a portion of another transducer 702
that includes piezoelectric transducer elements 2002 is shown. The
piezoelectric elements 2002 are a suitable substitute for the CMUT
elements 1902 described above and, when arranged in an array to
form a transducer 703 may have a top view substantially similar to
that of FIGS. 18A and 18B.
[0084] When viewed in the cross-section, the piezoelectric elements
2002 each include a chamber 2004 formed in the substrate 714. A
piezoelectric thin-film 2006 is formed over the chamber 2004.
[0085] Similar to the CMUT diaphragm 1504, the piezoelectric
elements 2002 can be quite thin. For example, in an embodiment, the
combined thickness 2008 of the piezoelectric thin-film 2006 and the
substrate 714 containing the chamber 2004 have a combined thickness
between approximately 5 .mu.m and approximately 10 .mu.m, with the
piezoelectric thin-film 2006 having a thickness between
approximately 1 .mu.m and approximately 2 .mu.m.
[0086] By connecting several elements in parallel, the embodiments
of FIGS. 19 and 20 provide an effective element size that is much
greater than the individual diaphragm size. This allows the
transducer to provide a more powerful ultrasonic signal while
transmitting and to produce a stronger electrical signal while
receiving. In addition, the operational frequency of a transducer
can be tuned by adjusting the number of elements operating in
parallel. The result is a more sensitive transducer in a smaller
package.
[0087] Thus, the present disclosure provides an improved IVUS
device with a scanner assembly that is designed to be both smaller
and more uniform, and provides a method for manufacturing the
scanner assembly improves yield and takes much of the complexity
out of the manufacturing.
[0088] Persons skilled in the art will recognize that the
apparatus, systems, and methods described above can be modified in
various ways. Accordingly, persons of ordinary skill in the art
will appreciate that the embodiments encompassed by the present
disclosure are not limited to the particular exemplary embodiments
described above. In that regard, although illustrative embodiments
have been shown and described, a wide range of modification,
change, and substitution is contemplated in the foregoing
disclosure. It is understood that such variations may be made to
the foregoing without departing from the scope of the present
disclosure. Accordingly, it is appropriate that the appended claims
be construed broadly and in a manner consistent with the present
disclosure.
* * * * *